High temperature pyrolysis and gasification of biomass and blends

Abstract

Biomass is expected to play an important role in the future because biomass can be gasified to produce syngas for the sustainable production of electricity, chemicals, and fuels. The research focus of this thesis was to provide a more fundamental understanding of four important parameters that affect biomass char gasification kinetics in a gasifier - pyrolysis conditions, biomass composition and inorganic content, interaction between two biomasses when co-fed together, and the gasifying media. The first study showed that higher pyrolysis temperature and higher residence time in a pressurized entrained flow reactor led to a decrease in char gasification reactivity. Furthermore, a complex char reactivity dependence on pyrolysis pressure is observed with minimum char reactivity at 15 bar (at 800 °C – 26 s – 5 to 20 bar). The second study correlated the reactivity of different types of biomass chars with its active surface area measured by CO2 chemisorption. This empirical correlation can be used for predicting the gasification reactivity of different biomass chars. The third study demonstrated that co-gasification of mixtures of Brazilian bagasse and cane trash was not additive. It was found that co-gasification of these two biomasses led to lower than expected gasification performance due to potassium redistribution between chars. The last study showed that the active sites for steam and CO2 gasification are likely to be the same. However, as the char gasification progresses in pure steam, the active sites are likely to be blocked by in-situ hydrogen product formation. It was demonstrated that product inhibition by hydrogen led to a different gasification reactivity profile in steam compared to CO2 during gasification of potassium containing bagasse char.